Food packaging containers such as thermoformed plastic containers are in widespread use in a varied and diverse number of household and commercial applications. Some food packaging containers are designed to be used in warming equipment so as to maintain the stored food at an adequate temperature. One such example is a storage container consisting of a talc filled polypropylene base with a lid made of oriented polystyrene which is designed to be used in a warming bin for warming a whole roasted chicken. One problem involved in using food packaging containers for food warming and/or display of hot foods is that condensation droplets form and the food packaging containers become fogged when the container contents are heated. The presence of obscuring fog limits the ability of the consumer to view the contents of the food packaging container, thereby obscuring the food contents and detracting from the marketability of the food product.
One method that has been used to alleviate fogging of food packaging containers during warming and/or display of hot foods has been to compound additives with the polymeric material used to make the container. In this method, the additives migrate to the container surface to reduce fog build-up. The additives are typically added to the polymer in concentrations ranging from about 1% to about 5% by weight. Examples include Glycolube PG and Glycolube AFA-1 available from Lonza of Fair Lawn, N.J. These types of additives, however, are typically useful only with containers made from polyethylene and polyvinyl chloride (PVC) and typically cannot be used with containers made from polystyrene. Materials that migrate to the surface require a matrix which allows sufficient molecular mobility to maintain a sufficient surface concentration of antifog agent to maintain a fog-free surface. Particularly in a warm environment, the antifog material is prone to being washed from the surface, and any additive used with the polymeric material would need to bloom very quickly to maintain adequate performance. While polyethylene and flexible PVC are typically used above their glass transition temperatures and experience efficient blooming, polystyrene is used well below its glass transition temperature which greatly slows the blooming process for polystryene.
Another method that has been used to alleviate fogging of food packaging containers during warming and/or display of hot foods has been to apply a coating of an antifogging nonionic surfactant blend to the surface(s) of the food packaging containers. The ability to apply a coating of an antifogging nonionic surfactant blend to the surface(s) of food packaging containers, however, is typically limited by the viscous nature of the antifogging nonionic surfactant blend. Antifogging nonionic surfactant blends are typically very viscous at room temperature, making a spray application without an extra heating step difficult. Another handling problem associated with antifogging nonionic surfactant blends involves solidification of these viscous materials at temperatures below ambient conditions. As a result, the antifogging nonionic surfactant blends must be stored in temperature-controlled environments so that the user may pump the antifogging nonionic surfactant blends from their storage containers.
Although heating these antifogging nonionic surfactant blends decreases the viscosity and alleviates some of the aforementioned handling problems, the spray pattern and coating weight of these blends often remain difficult to control even at elevated temperatures. This results in uneven coating of the food packaging container and requires the application of additional material to provide adequate coverage. This results in waste of material, variable product performance, and the use of excessive material on the food packaging container which can be unsightly. In addition, the heating step which is generally required to apply these antifogging nonionic surfactant blends involves additional processing steps and equipment, which increases the processing costs.
Accordingly, there exists a need for antifogging compositions that can be used on containers which are made from a variety of materials including polystyrene. There also exists a need for antifogging compositions that can be used to alleviate the formation of condensation droplets and fogging of food packaging containers during warming and/or display of hot foods while overcoming the processing and handling problems discussed above. There further exists a need for antifogging compositions that can be applied at room temperature without the processing and handling problems discussed above. In addition, a need exists for methods of using these antifogging compositions.